Encoding information in printed matter can be performed using, for example, bar codes or watermarking. In watermarking, information is hid in continuous-tone image data. Halftoning approximates continuous tone output on devices that are limited in their capability to render continuous tones. For example, halftoning is commonly used in printing where the digital marking engine of black and white printers can only render two levels, black when ink is printed and white (the color of the substrate) when no ink is printed.